Sudden temp swings

All was good until yesterday when the temperature started swinging. Spark is controlling heating element inside unitank and pump in water chiller, temperature of chiller is not controlled by Spark. Any setting I can tweak?

There are lots of things you can tweak, but the first step would be to figure out why this happens.

Can you please go to the cool/heat PID blocks, and post their graphs? You can access them either in the spark service page, or by clicking on the flame/snowflake icons in the layout.

Here is a graph of the cool and heat PID. It looks as if the change happened yesterday around 8 pm. This morning around 8 am I have raised the thermostat on the chiller so that the chilled water gradually raised to 11 celsius, this seems to have helped a little.

this is the updated graph for the beer temp

It looks like the D portion of one or both PIDs started overcompensating, leading to overcorrection on both sides, but it’s hard to say for sure, given that many of the graph lines overlap.

Could you please separate the Cool and Heat PIDs so the graph is less noisy, and zoom in on the period between ~1800 and ~0000?

Can you share your PID settings?
I would indeed first try with TD set to zero.

Looks like raising the water chiller temperature has helped in getting values back to normal.

Here is the updated graph and pid values.